Method and an apparatus for making a head on an elongate blank

ABSTRACT

In a method of making a head on an elongate blank (26), the blank (26) is moved into a die (16) having a bottom stop (28) such that part of the blank (26) extends outside the die (16) end opposite the bottom stop (28). The protruding part of the blank (26) is engaged by a pre-upsetting bushing (25) positioned in extension of the die (16) and a punch (27) is slidably movable in the pre-upsetting bushing. The bushing (25) and the die (16) are moved away from each other during the latter part of the deforming procedure. The movement of both the punch (27) and the bushing (25) with respect to the die (16) is positively controlled so that the bushing (25) and the die (16) are moved away from each other at the latter part of the deforming procedure, while the punch (27) continues to press against the blank in a direction toward the die (16).

FIELD OF THE INVENTION

The invention concerns a method and an apparatus for making a head on anelongate blank, wherein a blank is moved into a die having a bottom stopsuch that part of the blank extends outside the die end opposite thebottom stop. The protruding part of the blank is then formed by apre-upsetter which has a pre-upsetting bushing positioned in extensionof the die, and a punch capable of being displaced in the pre-upsettingbushing, said pre-upsetter and said die being moved away from each otherduring part of the forming procedure.

BACKGROUND OF THE INVENTION

For pre-upsetting of a head on an elongate blank it is known to place awire blank in a die having a bottom stop, e.g. in the form of an ejectorpin, following which the blank is formed by means of a punch in apre-upsetter.

To obtain optimum quality of the head and to avoid deflection of theblank during the upsetting process, it is of decisive importance thatthe free length of the wire blank between the die and the pre-upsetteris sufficiently small. Since, however, a large volume in the head isfrequently desired, this distance is usually increased to the maximumlength. It is frequently desired at the same time that pre-upsettingproceeds to a great diameter, which increases the load on thepre-upsetter pin. These circumstances limit the maximum upsetting ratiothat can be achieved, said upsetting ratio being the length of the wireoutside the retention of the die divided by the wire diameter. It isdesirable to achieve an upsetting ratio as great as possible.

It is known to improve the upsetting ratio by allowing the pre-upsetterto move away from the die during the process. This results in the shortdistance at the start of the process, while the length is increased witha simultaneous corresponding increase of the diameter during theprocess, whereby the blank remains stable. This takes place in the priorart by spring loading the pre-upsetter so that it is pressed away fromthe die as the head is formed. This prior art is mentioned e.g. byBilligmann/Feldmann: "Stauchen und Pressen", 1973. However, this processhas the drawback that it is difficult to optimize the process, becausethe movement of the pre-upsetter away from the die is only controlled bya spring, and this restricts the size of upsetting ratios that can beachieved.

In this prior art, the punch follows the forced movement of the formingmechanism from e.g. a crank mechanism.

SUMMARY OF THE INVENTION

The object of the invention is to provide a method and an apparatusmaking it possible to obtain considerably greater upsetting ratios thanhas been possible till now. Where the maximum upsetting ratio achievablein the past was about 5, it has been found possible to achieve aconsiderably higher upsetting ratio with the invention.

This is achieved in that the movement of both the punch and thepre-upsetter with respect to the die is positively controlled so thatthe pre-upsetter and the die are moved away from each other at the endof the forming procedure, while the punch continues to press in adirection toward the die. When the movement of the individual parts withrespect to each other is positively controlled in this manner, it ispossible to optimize the upsetting process much better than has beenpossible till now.

In one embodiment of the invention, the punch movement is controlled bya cam disc having pre-calculated curve paths. These curve paths arecalculated precisely so that the upsetting process will be optimum,because the movement of the punch does not follow the movement of theforming mechanism.

An apparatus for performing the method comprises means which canpositively control the movement of the punch as well as the pre-upsetterwith respect to the die, so that the pre-upsetter is moved away from thedie at the end of the working procedure, while the punch continues topress in a direction toward the die.

A particular embodiment of the apparatus comprises a cam disc havingpre-calculated curve paths for controlling the movement of the punch.

In a further the embodiment of the invention, the pre-upsetter isretained with respect to the base of the apparatus, and it is thus thepunch and the die which are moved with respect to the pre-upsetter. Thisprovides the advantage that the pre-upsetter may be a bushing which isalso used as a cropping bushing in the production of the employed blanksfrom a wire, and the further advantage that also the other tools used inlater process steps may be stationary with respect to the base of theapparatus.

When the bottom stop of the die is also movable, the blank can besubjected to pressure from both ends at the same time, enabling bettercontrol of the forming of the material.

The mentioned movements can be provided either by the provision ofseparate motors for each of the movements, or by a common motor whichproduces drives the various movements via various transmissions.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be described more fully below with reference to thedrawing, in which

FIG. 1 is a perspective view of a screw machine,

FIG. 2 is a sectional view of a cropping mechanism,

FIG. 3 is a perspective view of a cropping mechanism,

FIG. 4 shows the pre-upsetting process,

FIG. 5 shows an alternative pre-upsetting process,

FIG. 6 shows curve control of a pre-upsetting pin,

FIG. 7 shows an embodiment of the control from FIG. 6,

FIG. 8 shows an alternative embodiment of the control in FIG. 6,

FIG. 9 shows the second pre-forming of a screw head,

FIG. 10 shows forming of a slot in a screw head,

FIG. 11 shows the making of a screw point,

FIG. 12 shows the ejection of a blank from a die with a short ejectorpin,

FIG. 13 shows the ejection of a blank from a die with a long ejectorpin,

FIG. 14 shows the use of a slot detector,

FIG. 15 shows the making of a holding flange,

FIG. 16 shows a mechanism which converts a rotary movement to areciprocating movement,

FIG. 17 shows an alternative embodiment of the mechanism from FIG. 16,

FIG. 18 is a sketch of a crank and a connection rod,

FIG. 19 are curves showing motion and speed of a crank mechanism,

FIGS. 20A-20D shows how the die table can be controlled by a curve path,

FIG. 21 shows motion and speed of the die table and bottom stop withouttransition periods,

FIG. 22 corresponds to FIG. 21, but with inserted transition periods,

FIG. 23 corresponds to FIG. 22, but without a dwell period,

FIG. 24 shows the mounting of a die in a die table,

FIG. 25 is a section through a die table with a die, and

FIG. 26 shows how a die table can be constructed.

DETAILED DESCRIPTION

FIG. 1 shows an example of a screw machine in which the invention may beused. The machine is mounted on a base plate 1 and generally consists ofthree main parts, viz. a tool table 2, a forming mechanism 3 and a crankmechanism 4. The machine is driven by a motor 5 which is mounted on thebase plate 1.

The starting material for the making of screw blanks is a cold drawnwire 6, which is provided with a lubricating film on the surfaceoriginating from the drawing of the wire. The wire is drawn by means oftwo draw rollers 7, 8 having grooves corresponding to the employed wirediameter through a straightening device 9, which consists of a pluralityof straightening units 10, 11, 12, each of which being in turn providedwith a plurality of rollers 13.

The draw rollers 7, 8 move a given length of wire forwardly through astationary cropping bushing 14 and into a movable cropping bushingmounted in a rotatable cropping table 15. In a cropping process, whichwill be described more fully below, a wire blank is separated from thewire 6.

As will likewise be described more fully below, the wire blank is thenmoved into a die 16 which is mounted in a rotatable die table 17. Thedie table here has five dies and can rotate between five positions. Itis moreover axially movable. In a specific position of the die table 17,e.g. a movable cropping bushing in the cropping table 15 will be presentopposite the die 16. Correspondingly, tools will be mounted on the tooltable opposite others of the dies of the die table, said tools, incooperation with the dies, being capable of forming the screw blanksarranged in the dies. Forming takes place in that the die table 17 ismoved axially toward the tools in a working stroke. The die table 17 isthen withdrawn again, and it can rotate to the next position, followingwhich the process is repeated.

The rotating movement of the die table 17 can be established by a motor18 adapted for the purpose. Its axial movement is provided from thecrank mechanism 4 and is driven by the previously mentioned motor 5.Power transmission from the motor 5 to the crank mechanism 4 takes placeby means of a pulley 19 and a belt 20.

By means of two pulleys 21, 22 which are connected to a motor (notshown), the entire tool table 2 can be moved in a direction away from ortoward the die table 17, the tool table 2 being guided by a slide bar 23on the under side of the tool table and a corresponding one (not visiblein the figure) on the upper side. The tool table 2 can hereby beadjusted to its correct position, and it is also possible to draw thetool table away from the die table 17 in case of e.g. replacement oftools or die table.

The individual parts or processes in the machine will be described morefully below.

It is shown in FIGS. 2 and 3 how cropping and pre-upsetting take place.FIG. 2 is a cross-section of the constituent parts, while FIG. 3 is aperspective view.

The wire 6 is moved forwardly through the stationary cropping bushing 14and into a movable cropping bushing 24 which, as mentioned before, ismounted in a rotatable cropping table 15. The cropping table 15 has aplurality of movable cropping bushings 24, 25. When the wire 6 has beenmoved forwardly to the correct length, the rotatable cropping table 15is rotated, causing a wire blank to be separated from the wire 6.Further rotation of the cropping table 15 moves the movable croppingbushing forwardly to a position opposite a die 16, here shown at thecropping bushing 25. The released wire blank is here designated 26.

When the movable cropping bushing has been placed in this position, apunch 27 is moved forwardly toward the bushing and thereby pushes theblank 26 out of the movable cropping bushing 25 and into a die 16. Thismovement continues until the blank 26 hits a bottom stop 28, which ispositioned at the opposite end of the die 16. However, the punch 27continues its movement, whereby the blank 26 is pre-upset or pre-formedin the cavity between the die 16 and the movable cropping bushing 25.The punch 27 thus also serves as a pre-upsetting pin and the movablecropping bushing as a pre-upsetting bushing.

As described, so-called closed cropping is thus used here, thestationary cropping bushing as well as the movable cropping bushing 24having a hole corresponding to the diameter of the wire. In traditionalpresses or screw machines so-called open cropping is frequently used,comprising a stationary cropping bushing with a hole, whereas themovable bushing is open so that the wire blank is supported only in thedirection of travel. The closed cropping used here results in optimumquality of the separated blank. Since the quality of the finished objectdepends upon the quality of all the constituent processes, a higherquality of the separated wire blanks thus also means a higher quality ofthe finished objects.

The figures show two movable cropping bushings 24, 25 which are soarranged in the rotatable cropping table 15 that one is present oppositethe die 16 when the other is present opposite the stationary croppingbushing 14. However, more cropping bushings may advantageously bemounted in the cropping table 15. This will give a smaller angle ofrotation at each separation. Thus, if e.g. four movable croppingbushings are used, the cut wire blank will reach a position opposite thepunch or the pre-upsetting pin 27 and die 16 after two angular rotationsof the rotatable cropping table 15.

It is shown more clearly in FIG. 4 how the pre-upsetting processproceeds. As described before, the die 16, which is mounted in the dietable 17, is moved together with the associated bottom stop 28 in theaxial direction of the die. On the other hand, the movable croppingbushing 25 cannot be moved in the axial direction. FIG. 4A shows thesituation precisely at the time when pre-upsetting is initiated. Thepre-upsetting pin 27 pushes the wire blank 26 out of the bushing 25 andinto the die 16 such that the blank 26 reaches the bottom stop 28immediately before the die 16 at its turning point is in contact withthe pre-upsetting bushing 25. An expansion or countersink 29 of the holein the pre-upsetting bushing is provided at the end of the bushing 25facing the die 16. A corresponding expansion or countersink 30 isprovided in the die 16. These countersinks define cavities which enablethe pre-forming of a head on the wire blank 26.

These cavities are shaped so that the free length 1 of the wire blank 26will be as small as possible with respect to the diameter d of theblank. The pre-upsetting pin 27 is controlled so that pre-upsettingcontinues after the die 16 has again initiated its movement away fromthe bushing 25. This gives an increased height of the pre-upset whileincreasing the diameter of the pre-form, so that the volume of thepre-formed material can be increased without the pre-form becomingunstable, so that the upsetting ratio is not restricted by the process.The upsetting ratio is the head wire length divided by the wirediameter. FIG. 4B shows the situation at the termination of thepre-upsetting process. The pre-formed head now has the height L and thediameter D. In addition to a greater upsetting ratio, this method alsoresults in reduced loads on the pre-upsetting pin. FIG. 5 shows analternative embodiment, using instead of the bottom stop 28 a movablebottom stop, e.g. in the form of an ejector pin 31 which can be movedwith respect to the die 16. It will hereby be possible to control theprocess even better.

For the process shown in FIG. 4 to be optimized, the movement of thepre-upsetting pin 27 must be controlled very precisely with respect tothe movement of the die 16. FIG. 6 shows an example of how this can bedone. The previously described parts are shown to the right in thefigure. It will be seen that the die 16 and the bottom stop 28 are beingmoved away from the bushing 25, so that a head 32 will be formed on thewire blank, the punch or pre-upsetting pin 27 still pressing in adirection toward the die 16. A roller 33 is provided at the end of thepre-upsetting pin 27 and is in contact with the surface of a cam disc34. The cam disc 34 rotates about the axis of rotation 35, and the camdisc 34 is constructed such that the desired movement of thepre-upsetting pin 27 is achieved.

FIG. 7 shows an example of how the mentioned movements can be provided.The reciprocating movement of the die 16 is here provided by a crankmechanism 36 which is driven by a motor 37 by means of a belt 38. Themovement of the pre-upsetting pin 27 is provided by another motor 39which drives the cam disc 34 via another belt 40, thereby transferringthe desired movement via the roller 33 to the pre-upsetting pin 27.

Alternatively, as shown in FIG. 8, the two movements can also becontrolled by a common motor 41. This motor drives, via a belt 42, thecrank mechanism 36 which transfers the movement to the die 16. By meansof another belt 43 the same motor drives the cam disc 34 which transfersthe movement to the pre-upsetting pin 27 via the roller 33.

When the pre-upsetting process, which can also be called firstpre-forming here, has been terminated and the die table 17 has beendrawn back, the table can be rotated to a new position. In theembodiment of the rotatable die table 17 shown in FIG. 1, where saidtable comprises five dies 16, the die table will now be rotated 72°, sothat a new die is moved forwardly to the position opposite a movablecropping bushing, while the die having Just been present here is movedforwardly to a new position. When the die table 17 is again movedforwardly toward the tool table 2, the process described above will berepeated at the cropping or pre-upsetting bushing, while further shapingof the blanks arranged in the dies will take place at the other diepositions.

FIG. 9 shows an example of a process which can follow the pre-upsettingprocess described above. The process shown here is called secondpre-forming. FIG. 9A shows the situation at the beginning of thisprocess, while FIG. 9B correspondingly shows the situation immediatelyafter it has been completed. In FIG. 9A a blank is placed in a die 45which, together with a bottom stop 46, is moved toward a tool 47. Thetool 47 is positioned stationarily on the tool table 2, while, asdescribed before, it is the die 45 arranged in the die table 17 whichmoves toward and then away from the tool 47. When the head on the blank44 hits the tool 47, it will be formed to the desired shape by adepression 48 in this tool. It is shown in FIG. 9B how the blank 44 hasnow been formed to the blank 49 shown here. The blank 49 together withthe die 45 and the bottom stop 46 are being moved away from the tool 47.

FIG. 10 correspondingly shows a forming that may take place at a thirddie position. In this process a slot or the like is produced in thescrew head just formed. The blank 49 is now present in a die 50 which,together with a bottom stop 51, is moved toward a tool 52. The tool 52is provided with a slot projection 53 which forms a slot in the head ofthe blank 49. FIG. 10A shows the situation at the start of the process,while FIG. 10B shows the situation at the termination of the process,the numeral 54 designating the blank with the slot now produced.

Many types of blanks are moreover to be provided with a so-called point,which may e.g. have the shape of a truncated cone at the end of theblank opposite the head. FIG. 11 shows an example of how such a pointcan be produced simultaneously with the provision of the slot in thehead of the screw. FIG. 11 corresponds to FIG. 10A, there being justused a bottom stop 55 here which is provided with a frustoconical cavity56 arranged in direct extension of the through hole in the die 50. Thehead on the blank 49 has been shaped in the previously pre-formingprocess such that there is an excess of material with respect to thesize of the finished head on the screw. When the slot projection 53 hitsthe head on the blank 49, it presses the excessive material down throughthe shank of the blank. Thus, flow of material will take place in theentire length of the blank, and the material will be pressed out intothe frustoconical depression 56 in the bottom stop 55.

It will be appreciated that it is possible to produce many differenttypes of points in this manner, since the depression 56 can be given ashape that corresponds to the desired point type. It may be mentioned inparticular that it will be possible to produce a hemispherical point,which required a separate process in the past. This is a simple mannerof producing a point, and the flow of material down through the shank ofthe blank moreover causes the load on the tool 52 to be minimized, whilethe tolerances of the slot will be smaller. The method can also beapplied in the production of screws without points. In that case, thedepression 56 is shaped as a cylindrical depression having the samediameter as the hole in the die 50, or a bottom stop with a projectionextending into the die may be used, said bottom stop being then merelymoved slightly backwards from the die when the slot projection 53produces the slot in the head of the blank.

An interesting aspect of the mentioned flow of material down through theshank of the blank is the part of the flow that takes place at thetransition between the head and shank of the blank. The reason is thatthis flow has been found to strengthen the weak point which, otherwise,is traditionally found in screws at this transition.

In case of certain types of points it may be necessary or advantageousto produce the point in two steps. If so, a first depression is shapedin the bottom stop 46 which is used in the second pre-forming of thehead of the screw blank.

It is described above how a blank can be formed in three die positions.This, however, is merely an example, since the three positions may beused flexibly depending upon the shape of the desired objects, or ifnecessary, more than three positions may be used for the forming.

In the machine shown in FIG. 1 with five dies in the die table 17 andthus correspondingly five positions for each die, the last two positionsmay be used for ejection of the blank, and this ejection can then takeplace in two steps. FIG. 12 shows the first step of this ejection andthus corresponds to the fourth die position. A blank 57 placed in a die58 is visible at the top of the figure, which shows the situationimmediately before ejection. A bottom stop 59 with a short ejector pin60 is being moved toward the die. At the bottom of the figure, thebottom stop 59 with the short ejector pin 60 has reached the die 58, andthe ejector pin 60 has loosened the blank 57 and pushed it a short andwell-defined distance out of the die 58. Because of the precedingprocesses the blank 57 will often be very firmly fixed in the hole ofthe die, and a very great force is therefore required to release theblank and push it out of the die. If the blank should have been pushedout of the die in one operation, this would have required an ejector pinwhich had the same length as the die, and this would therefore involve avery great risk of pin bending or breaking. Since the short ejector pin60 can release the object with a great force without any risk ofdeflection, release of the blank from the die need not be facilitated bymeans of lubrication or the like.

FIG. 13 shows how the blank 57 is then ejected completely from the die58 at the fifth and last die position. This takes place in that a bottomstop 61 with a long ejector pin 62 pushes the blank out of the die. Theejector pin 62 has approximately the same length as the die 58 and thusas the blank 57. The top of the figure shows the bottom stop 61 and thelong ejector pin 62 on their way toward the die 58, and at the bottom ofthe figure the bottom stop 61 and the ejector pin 62 have pushed theblank 57 completely out of the die 58. Since the blank 57 having beenreleased in the preceding die position by means of the short ejector pin60, is now positioned relatively loosely in the die, only a modest forceis required to eject the blank completely, and the long ejector pin 62will therefore not tend to break or bend.

Both the short ejector pin 60 and the long ejector pin 62 may have thesame diameter as the shank of the blank 57, since an optional point onthe blank 57, as described before and shown in FIG. 11, will be producedby means of a depression in the corresponding bottom stop 55. In thepast, it was necessary to produce such a point by making a constrictionin the die itself, and an ejector pin could only have a diametercorresponding to the narrowest portion of the die.

Since, as shown in FIG. 12, the short ejector pin 60 pushes the blank 57a short and well-defined distance out of the die, this may be utilizedfor controlling the blank produced. FIG. 14 shows an example of how thismay be done. The figure corresponds to FIG. 12, but includes a slotdetector 63 comprising a control bit 64 which is arranged at a carefullydetermined distance from the die 58. The slot detector 63 is connectedvia a connection wire 65 to electronic equipment capable of processingthe signals emitted from the slot detector 63. It is shown at the bottomof the figure how the short ejector pin 60 has pushed the blank 57 outof the die 58, and that the blank contacts the control bit 64. If theslot projection 53, by means of which the slot in the screw was made,has e.g. been damaged, the slot may be too small, and the blank 57 willthen exert a pressure against the control bit 64. This is registered bythe slot detector 63 which transmits signals about this to a controlunit via the connecting wire 65. Thus, in this manner it is possible tocontrol the geometry of the produced blanks.

Since the blank has been pushed out of the die, it is also possible tocontrol e.g. the height or diameter of the head in addition to apossible slot.

Furthermore, the distance between the die and the tool table may bedetected, and the signals from the detector 63 may be used for adjustingthe tools. When the machine starts from a cold state, the machine partswill be heated owing to the processes in the machine and these partswill be thermally expanded at the same time. It may therefore be anadvantage that these expansions can be allowed for by adjusting theposition of the tools with respect to the dies in the die table 17. Thiscan be done since, as mentioned before and shown in FIG. 1, it ispossible to displace the entire tool table 2, and when such adisplacement is effected in response to the control signals from thedetector 63, a more uniform quality will be obtained which is notdependent on thermal heating in the machine.

The shown slot detector is just one of the many available possibilitiesof making a control measurement of the blanks produced. Measurements ofother geometrical properties of the produced objects can be made, and itis also conceivable to make the measurement in other ways. Thus, e.g. ameasurement may be made by means of laser beams so that the detectorneed not be in contact with the produced objects.

When e.g. a slot is made in a head on a blank, as described above andshown in FIG. 10, there is a certain risk that the slot toolunintentionally pulls the blank out of the die. This can be counteractedas shown in FIG. 15. Here, a blank 66 positioned in a die 67 and abottom stop 68 are visible. The blank has a head 69 at one end, and itwill be seen that a small holding flange 70 is provided at the oppositeend of the blank. The flange is provided in that the die 67 at this endhas a small expansion of the through hole. The pre-upsetting process,which has been described and is shown in FIG. 4, also causes material tobe pressed out into this expansion, thereby making the flange 70.However, the flange does not necessarily extend all the way round theblank, since a smaller projection on the blank will be sufficient toperform the desired function, viz. to protect the blank against beingpulled out of the die at an unappropriate time. The flange or theprojections are just large enough to prevent this and also small enoughfor an ejector pin, in the subsequent ejection of the blank, to be ableto deform the flange or the projections and eject the blank from thedie.

It is shown in FIG. 16 how the reciprocating movement of the die table17 and the associated bottom stops can be established. As describedbefore and shown in FIG. 1, this axial movement is provided by a motor5, and the power transmission from the motor 5 takes place via belts 19,20 and a crank mechanism 4. FIG. 16 shows in greater detail how thismechanism is constructed.

A crank 71 rotates about its axis of rotation 72 and is driven by thebelt 20, as mentioned. A connecting rod 73 is secured to the crank 71 atone end and to a holder 74 at the other. When the crank 71 rotates, therotating movement is converted via the connecting rod 73 to areciprocating movement of the holder 74. The holder 74 is connected withtwo wedges 77, 78 via two rods 75, 76 such that these wedges, too, canbe reciprocated. For this reciprocating movement to take place with avery small friction, a plurality of rollers 81 and 82, respectively, arepositioned between the wedges 77, 78 and guide rails 79, 80. A bearingblock 83 is interposed between the two wedges 77, 78, which is capableof being moved in a direction transversely to the direction of travel ofthe wedges. This movement, too, can take place with a very smallfriction, because rollers 84 and 85, respectively, are arranged betweenthe bearing block and the guide rails 86, 87. Finally, a plurality ofrollers 88 are also provided between the bearing block and the wedge 77as well as a plurality of rollers 89 between the bearing block 83 andthe wedge 78. When the wedges 77, 78 are moved to the left in thefigure, the bearing block 83 will be moved in a downward direction inthe figure because it can only move in the transverse direction. Whensimilarly the wedges are moved to the right, the bearing block 83 willbe moved upwardly. The bearing block 83 thus moves to and fro in adirection transversely to the corresponding movement of the wedges.

It will be seen that the wedge angle selected in the figure will causethe movement of the bearing block to be smaller than that of the wedges.The bearing block 83 is connected via connections (not shown) with thedie table 17 and the associated bottom stops, respectively.

In this manner the die table 17 can perform a relatively shortreciprocating movement, it being simultaneously possible to exert greatforces which are necessary in the forming of the blanks positioned inthe dies. Because of the wedge angle shown in the figure the wedges andthereby the crank mechanism will perform a greater movement, but then asmaller force is required, and the crank mechanism can therefore bedimensioned smaller than would otherwise be necessary.

The rollers 81, 82, 84, 85, 88 and 89 shown in FIG. 16, which serve toreduce the friction between the individual components, may also haveother shapes. Thus, e.g. balls may be used instead. An alternativeembodiment is shown in FIG. 17 in which slide guides are used instead.The slide guides 90, 91 reduce the friction between the wedges 77, 78and the guide rails 79, 80, while the slide guides 92, 93correspondingly reduce the friction between the bearing block 83 and theguide rails 86, 87. Finally, the slide guides 94, 95 serve to reduce thefriction between the bearing block 83 and the wedges 77, 78.

It is of great importance that the production rate of a machine of thetype described here can be as high as possible. At the same time, thespeed of the die at the beginning of the actual forming should be as lowas possible. This is achieved i.a. by using a wedge mechanism, asdescribed above, the wedge angle being selected such that the movementof the bearing block and thereby of the die table has a relatively smalllength of stroke. Furthermore, the velocity at which the die tableapproaches its extreme positions in such a movement differs. This isshown in FIGS. 18 and 19.

FIG. 18 schematically shows a crank mechanism. The crank rotates aboutan axis of rotation C. At its one end a connecting rod of the length ais secured to the crank at a distance r from its center or axis ofrotation. Rotation of the crank causes the point P, which designates theother end of the connecting rod, to perform a reciprocating movement onthe horizontal line. 1 designates the distance from the axis of rotationC to the point P. The distance 1 is shown at the top of FIG. 19 as thefunction of time at a constant crank speed of rotation. If the length ais very great with respect to the distance r, the point P will perform apure sine movement, which is shown with the first of the two curves. If,on the other hand, the length a is short with respect to the distance r,the sine curve will be distorted. The smaller a is with respect to r,the more pronounced the distortion is. In the extreme case where a isequal to r, the point P will lie still for half of a period of rotation.The other curve at the top of FIG. 19 shows the movement of the point Pin the situation where a is equal to 1.2 times r. It will be seen thatthe point P relatively slowly approaches the extreme position which ispassed at the time t1, while, on the other hand, it relatively quicklyapproaches the other extreme position, as shown at t0 or t2. The bottomof FIG. 19 correspondingly shows the speed of the point P as a functionof time for the same two situations. It is even more clearly visiblefrom this that the point P approaches one extreme position at arelatively low speed and the other extreme position at a relatively highspeed. To achieve the lowest possible working rate for a givenproduction rate, the die table is therefore connected with the bearingblock 83 such that forming of the blanks mounted in the dies takes placeat that one of the extreme positions of the die table where itapproaches the position at the lowest speed.

As described before, the die table 17 and the associated bottom stopsare moved as a common unit towards the tools at the forming moment andthen away from these again. However, at the opposite extreme positionthe die table must be separated from the bottom stops for the die tableto rotate to a new position. This can be done by mounting a stop meanswhich prevents the die table from following the bottom stops to theirextreme position. This, however, will give rise to generation of muchnoise and great wear on the die table, partly when the die table hitsthe stop means, and partly when the bottom stops again hit the die tableon their way back. This problem can be remedied by inserting transitionperiods where the die table is slowed down before hitting the stop meansand is accelerated before being hit by the bottom stops.

It is shown in FIGS. 20A-20D how this can be done through the aid of acam means 96. In FIG. 20A the die table 17 is shown in the extremeposition in which it is in contact with the tools, here e.g. the tool98. As will be seen from the figure, a bottom stop 97 is in contact withthe die table 17 at its opposite end. The cam means 96 is provided witha curve path 100, and it is moved in a direction transversely to theaxial direction of travel of the die table. It is shown by arrows in thefigure that the die table 17, after the contact with the tool 98, ismoved away from it in the direction of the arrow while the cam means 96is moved in an upward direction. As will be seen from the figure, thecam means 96 is provided with a curve path 100, while a roller 99 ismounted on the die table 17.

FIG. 20B shows the situation where the die table 17 together with thebottom stop 97 has been moved away from the tool 98 and is about to hitthe cam means 96, which continues its upwardly directed movement. InFIG. 20C, the roller 99 has contacted the curve path 100. The curve path100 is shaped such that together with the speed of the cam means 96 itentails that the die 17, immediately after contact between the roller 99and the curve path 100, will continue at an unchanged velocity and isthen slowly braked. It will be seen from the figure that the bottom stop97 continues its movement and is therefore no longer in contact with thedie table 17. FIG. 20D shows the situation in the extreme position whereboth the die table 17 and the bottom stop 97 are removed from the tools.The die table 17 is now separated from the bottom stop 97 and can rotateto a new position. Then the process proceeds in the opposite direction.The bottom stop 97 is moved forwardly toward the die table 17, which issimultaneously accelerated because of the cooperation between the curvepath 100 and the roller 99, the cam means 96 now moving in a downwardlyextending direction. Owing to the shape of the curve path 100 the dietable 17, when being hit by the bottom stop 97, will have attainedprecisely the speed which the bottom stop has at this moment.

FIGS. 21, 22 and 23 show the movement and the speed of the die table 17and the bottom stop 97, respectively, in three different situations. Thetops of the figures show the movement expressed by the distance A fromthe tools. The movement of the bottom stop 97 is shown in thin line,while the movement of the die table 17 is shown in thick line. Thebottoms of the figures correspondingly show the velocity (V) of thebottom stop in thin line and of the die table in thick line.

FIG. 21 shows the situation where there is no transition period, so thatthe die table 17 merely hits a stop means on its way away from the toolsand is then hit by the bottom stop on its way toward the tools. Themovement of the bottom stop is here shown as a pure sine curve. Asmentioned above, this will be the case only if a connecting rod having avery long length with respect to the size of the crank is used. Thecorrect curve will be distorted as shown in FIG. 19. It will be seenthat for half a period the die table will be present in a dwell positionwhere it can be rotated, while the bottom stop continues with a harmonicmovement to its extreme position and then returns.

In FIG. 22, transition periods are inserted between the working periodwhere the die table 17 moves together with the bottom stop 97 and thedwell period where the die table stands still.

FIG. 23 shows a situation where the transition periods have been madevery long so that the dwell period is short or zero. This has theadvantage that also the die table 17 performs a harmonic movement and istherefore subjected to the lowest possible forces in the axial directionbecause of the movement.

FIG. 24 shows a section of a die table 101 in which a die 102 ismounted. A band winding 103 is applied around the die 102. This bandwinding has been provided by winding a steel band around a cylindricalcore, which may either be the die 102 itself, which is made of hardmetal, or a cylindrical insert. The band winding 103 biasses the die 102by absorbing the outwardly directed forces which occur when the die 102is subjected to strong compressive stresses in the axial direction.

FIG. 25 shows a section through part of the die table 101, and it isshown more clearly in this section how the die 102 may be mounted in thedie table 101. The die 102 here has a conical shape and is mounted in abushing 104, whose interior has a conical shape corresponding to that ofthe die. The bushing 104 is wound with the band winding 103, which is inturn placed in a suitable hole in the die table 101. This structure hasthe advantage that the die 102, because of the conical shape, can easilybe replaced by pressing it out of the bushing 104. A new die can bepressed down into the conical bushing 104 and thus ensure that the dieis biassed correctly.

The advantage of biassing the hard metal die in this manner by means ofa band winding is that the die unit, including bias, can be given a verysmall cross-sectional area. This means that the dies in a die table canbe positioned more closely to the axis of rotation of the die table andthus contribute to reducing its moment of inertia. FIG. 26 shows anexample of the shape of a die table 101. In this case the die table hasfive dies, all of which are biassed by means of band windings asdescribed above. For a high production rate to be achieved, the dietable must have as low a moment of inertia as possible. This is achievedpartly in that the dies, including bias by means of band windings, havea modest extent, and partly because they can then be positioned moreclosely to the axis of rotation 105 of the die table. The moment ofinertia of the die table is then additionally diminished by a recess 106between each die, such that the die table has the shape of a cloverleaf. This contributes to reducing the moment of inertia of the dietable considerably, because precisely that portion of the material isremoved which is most remote from the axis of rotation 105 and therebycontributes most to the moment of inertia.

Further, it also contributes to reducing the moment of inertia that dieshaving the same length as the blanks are used here. The known machinesusually employ longer and thus heavier dies.

The small moment of inertia entails that the die table can be drivendirectly by a servomotor having a high production rate.

The foregoing description gives examples of how a machine according tothe invention can be constructed, and it will be appreciated thatdetails in the described and shown matter can be modified in many wayswithin the scope of the invention.

What is claimed is:
 1. A method of forming a head on an elongate blank,comprising the steps of:moving an elongated blank into a die having abottom stop such that one end of the blank contacts the bottom stop andan opposite portion of the elongated blank extends from the die at anend thereof opposite said bottom stop, engaging said portion of theblank extending from the die by a pre-upsetting bushing positioned inextension of the die, slidably moving a punch in said pre-upsettingbushing to engage said blank and apply pressure thereto, providingrelative movement between said pre-upsetting bushing and said die awayfrom each other while applying said pressure to the blank by said punchto form a space between the pre-upsetting bushing and the die and todeform a portion of the blank into said space, said portion of the blankwhich is deformed forming a head for said blank, and controllingrelative movement of both the punch and the pre-upsetting bushingpositively with respect to the die so that during a final part of thedeforming of said portion of the blank, said pre-upsetting bushing andsaid die are moved away from each other to form said space, while saidpunch continues to move relative to said die and apply pressure to saidblank in a direction toward the die whereby said deformed portion of theblank is produced in said space between the die and the bushing.
 2. Amethod according to claim 1, wherein the movement of the punch iscontrolled by rotating a cam disc having a predetermined cam surface. 3.A method according to claim 2, wherein the movement of the die iscontrolled by operating a crank mechanism connected to said die.
 4. Amethod according to claim 3, comprising driving the cam disc and thecrank mechanism separately and independently of one another.
 5. A methodaccording to claim 3, comprising driving the cam disc and the crankmechanism from a common drive means.
 6. A method according to claim 1,comprising disposing said bushing and said die in proximity to oneanother while said punch applies pressure to said blank at the beginningof deforming of the blank.
 7. An apparatus for forming a head on anelongate blank, said apparatus comprising:a die having a bottom stop anda through hole for receiving an elongated blank such that one end of theblank contacts said stop and an opposite end portion of the blankextends outside the die at an end thereof opposite the bottom stop,pre-upsetting means for deforming the portion of the blank extendingoutside the die to produce a deformed portion from which a head can beformed on the blank, said pre-upsetting means comprising a pre-upsettingbushing in extension of the die and a punch slidably movable in thepre-upsetting bushing to engage an end of said portion of the blankextending from the die and apply pressure to the blank, and means forpositively controlling relative movement of both the punch and thepre-upsetting bushing with respect to the die so that during a finalpart of the deforming of said portion of the blank, said pre-upsettingbushing is moved away from the die to form a space between the die andthe pre-upsetting bushing, while the punch continues to move withrespect to the die to apply pressure to the blank in a direction towardthe die to deform said portion of the blank in said space between thedie and the pre-upsetting bushing.
 8. Apparatus according to claim 7,wherein said means for controlling movement comprises a rotatable camdisc controlling movement of said punch.
 9. Apparatus according to claim8, wherein said means for controlling movement further comprises a crankmechanism connected to said die for moving said die relative to saidbushing.
 10. Apparatus according to claim 9, comprising separate drivemotors to drive said cam disc and said crank mechanism respectively. 11.Apparatus according to claim 9, comprising a single drive motor andmeans connecting said drive motor to said cam disc and said crankmechanism.
 12. Apparatus according to claim 9, wherein said bottom stopis separate from said die and is coupled to said die for common movementtherewith.